Hello @Shiroo, and welcome to the forum!
Look through this bundle:
Sketch V2. (SK2) Pleasure to draw. including colored pencils and blenders
And here you can find tons of brushes for most needs:
Make sure to always scroll down to the very end, then the page loads the next load of resources.
Since we do not know what kind of rendering you have in mind, but perhaps you may want to try the bundles from @Rakurri and @fizzyflower.
Michelist